Placenta, the. Placentals, the. characters of the. gastrulation of the. Planocytes. Plant-louse, parthenogenesis of the. Planula, the. Plasma-products. Plasson. Plastids. Plastidules. Platodaria. Platodes, the. Platyrrhinae. Pleuracanthida. Pleural ducts. Pliocene strata. Polar cells. Polyspermism. Preformation theory, the. Primary period, the. Primates, the. Primatoid. Primitive groove, the. gut, the. kidneys, the. mouth, the. segments. streak, the. vertebrae. Primordial period, the. Prochordata. Prochordonia, the. Prochoriata. Prochorion, the. Proctodaeum, the. Procytella primordialis. Prodidelphia. Progaster, the. Progonidia. Promammalia. Pronephridia, the. Pronucleus femininus. masculinus. Properistoma. Prorenal canals of the lancelet. duct, the. evolution of the. Proselachii. Prosimiae, the. Prospermaria. Prospondylus. Prostoma. Protamniotes. Protamoeba. Proterosaurus, the. Protists. Protonephros. Protophyta. Protoplasm. Protopterus. Prototheria. Protovertebrae. Protozoa. Provertebral cavity, the. plates, the. Pseudocoela. Pseudopodia. Pseudova. Psychic life, evolution of the. Psychology. Pterosauria. Pylorus, the. Quadratum, the. Quadrumana. Quaternary period. Rabbit, ova of the. Radiates, the. Rathke's canals. Rectum, the. Regner de Graaf. Renal system, evolution of the. Reproduction, nature of. Reptiles. Respiratory organs, evolution of the. pore, the. Retina, the. Rhabdocoela. Rhodocytes. Rhopalura. Rhyncocephala. Ribs, the. number of the. Rudimentary ear-muscles. organs. list of. toes. Sacculus, the. Sagitta. coelomation of. Salamander, the. ova of the. Sandal-shape of embryo. Satyrus. Sauromammalia. Sauropsida. Scatulation theory, the. Schizomycetes. Schleiden, M. Schwann, T. Sclerotic coat, the. Sclerotomes. Scrotum, the. Scyllium, nose of the. Sea-squirt, the. Secondary period, the. Segmentation. Segmentation-cells. Segmentation-sphere, the. Selachii. skull of the. Selection, theory of. Selenka. Semnopitheci. Sense-organs, evolution of the. number of the. origin of the. Sensory nerves. Serocoelom, the. Serous layer, the. Sex-organs, early vertebrate form of the. evolution of the. Sexual reproduction, simplest forms of. selection. Shark, the. nose of the. ova of the. placenta of the. skull of the. Shoulder-blade, the. Sickle-groove, the. Sieve-membrane, the. Silurian strata. Simiae, the. Siphonophorae, embryology of the. Skeleton, structure of the. Skeleton-plate, the. Skin, the. evolution of. function of the. Skin-layer, the. Skull, evolution of the. structure of the. vertebral theory of the. Smell, the sense of. Soul, evolution of the. nature of the. phylogeny of the. seat of the. Sound, sensations of. Sozobranchia. Space, sense of. Species, nature of the. Speech, evolution of. Spermaducts. Spermaries, evolution of the. Spermatozoon, the. discovery of the.